Electric cable



I May 10, 1938. H ROST 2,116,643

ELECTR IC CABLE Filed July 19, 1933 Fyff f5@- j-Tf-ff- One of" moreagg/U 'L'c Pd, I 5 fm 'm fm2 gyde/ro para /72eZ2zZ fg/ 5l jc 7.

A L u A Helge ROS* INVENTOR BY @MKM fuk ATroRNEY.

Patented May 1o, 193s UNITED STATES PATENT OFF-KCE:

Application July 19, 1933, Serial No. 681.186 In Germany February 15,1932 8 Claims.

This invention relates to improvements in electric cables.

Present day cables for telephony.. telegraphy and low tension currentsin genral have many deficiencies, among which are the following:

The great hygroscopic content of the paper insulation of the individualconductors causes absorption of moisture from air with a corre-'sponding lowering of the insulating eiciency and increase of capacitybetween conductors.

Expensive machinery is necessary to create a vacuum or drying of theair. paper and cable beicre the cable sheath is put on, withcorresponding loss of time.

y During jointing and repairing oi' paper insulated cables, the. utmostprecautions must be observed, so that the paper does not absorb moistureand usually a hot cable compound is poured over the Joint. in order toavoid absorption of moisture as much as possible.

U Uneven insulation will result. as peper normally contains 7 to 12 percent. of moisture while paper specially dried inside the cable containsat least 0.5 per cent. moisture. 1n the neighbor hood of a. joint, thismoisture content is materially increased by absorption when the cablesheath is removed and this is specially the case when the air is chargedwith moisture. The joint proper will have very different values ofdielectric constant of the impregnated insulating material, as well asthe capacity and insulation between the conductors, when compared withthe dry cable. Possibilities of unbalances and cross currents willeventually exist between diierent conductors oi such a cable.

Cables, the conductors oi' which are insulated with vulcanized rubber,impregnated cotton, silk. etc., have too great a capacity withcorresponding limitation of the speed of transmission.

lo Cables have also been proposed in which the conductors are surroundedby air and enclosed in a. paper insulation or an insulating materialconsisting of vulcanized rubber, ebonite or gutta perche.

The lead sheath is heavy with very low tensile strength. The lead lacksan elastic limit. and on that account repeated temperature variatonsleave microscopic fractures in th sheath. The lead crystalllzes or ages.On a count of the 50 great softness oi lead, the'sheath is exposed toall kinds o! damage, for instance when the cable is pulled in andl outof underground' ducts,

mounted on or taken down from aerial pole lines.

There are also in many countries plagues of 55 small beetles thatperiorate the lead sheath.

According to the present invention. the abovementioned inconveniencesare entirely eliminated, a cable for communication purposes beingmanufactured in the following way:

Each metallic conductor is provided with an insulation consisting of oneor more layers of insulating tape of a non-hygroscopic. homogeneous,synthetic organic compound. which are wound loosely and spirally aroundthe conductor` with or without the application of adhesive to theoverlap, preferably in the form of a solvent lo of the film, oralternatively the insulation may consist of one or more continuoussleeves of cylindrical or other section of such insulating materialplaced over the conductor, which sleeves Y: are formed by means of oneor more mouthpieces by extrusion of the compound, which at hightemperatures is plastic and when cooled becomes solid. Between theconductor and respective sleeves air spaces are left. Depending upon thematerial one sleeve can be extruded at a time or 90 severalsimultaneously by one or several mouthpieces, as shown m the. annexeddrawing in which- Fig. l is a transverse seul-.ion oi a single convductor cable; 2e

Figs. 2 and 3 are transverse sections of twinconductor cables:

Figs. 4 and 5 are transverse sections of multiconductor. cables;

Fig. 6 is a perspective view of an insulating sleeve enclosing aconductor and provided with protuberances for centering the same;

Figs. 7 and 8 are transverse sections on lines B-B and A-A of Fig. 6,respectively.

The insulating material consists of an organic tough, flexible,homogeneous, waterproof and plastic compound of synthetic origin, whichis non-hygroscopic and contains no hydroxyl groups, for instance: 40

Polymerization products obtained from chemical compounds comprising thevinyl group (-CHzCHz), like polymerized vinyl-benzene, polystyrol. etc.

The above-mentioned polymerization products 45 and particularly thosewhich like polymerized vinyl benzene belong to the group of substitutedbenzenes of which each substitute radical comprises a vinyl group areespecially suitable insulating materials for conductors forcommunica-.50 tion purposes in accordance with the present invention.Particularly suitable are also those substances whichl like polystyrolbelong to the groupl of aryl oleiines. These materials, in the purestate, have a very nigh insulating resistance, 5s

an extraordinary low phase angle difference, and an exceptionally lowdielectric constant thus causing very small dielectric losses. Moreover,the above mentioned materials are substantially non-hygroscopic andtherefore have stable electric properties, lwhich remain unchanged bymoisture.

In order to lessen the capacity between the conductors the surface ofthe insulating film or sleeve may be embossed or provided with regularprotuberances and recesses, whereby greater air spaces are obtainedaround the respective conducti-rs.

In this way the advantage is also obtained in certain cases that theconductors are in contact with the insulation over a small portion onlyof their length, and can be located in the middle of the respectivesleeves and at the same distance from the walls of the sleeve, as shownin Figs. 6, '7 and 8.

In order to keep the capacity as low and even as possible between thepairs of twinor quadgroups and in order to avoid irregularities of thedistance between the respective conductors and groups of conductors,which irregularities would cause cross-currents, any of the arrangementsshown in Figs. 2, 3, 4 or 5, may be used, which figures only areexamples of how the conductors can be placed in order to be located atpredetermined and equal distance from each other, but other combinationsmay-be used to obtain the same result. Fig. 1 shows an electricconductor provided with a cylindrical sleeve. Fig. 2 shows twoconductors arranged in the form of a twingroup with an insulatingpartition between the respective conductors, and both conductorsenclosed in a common cover. 'I'he cover and the partition can beextruded simultaneously around the respective conductors, whereafter thewhole group is formed before the 4plastic compound has got entirelysolid.

Fig. 3 shows another form of twin-group, simi-- lar to that of Fig. 2,but with greater distance between the conductors in order to lessen thecapacity between them.

Figs. 4 and 5 show examples of how quadgroups can be arranged accordingto the extrusion method. whereby the individual conductors always keepthe same distance between each other and between the conductors ofadjoining groups, and whereby the greatest possible air spaces areobtainable. I is a conductor, 2 is a continuous, preferably hollow,insulating core of suitable cross section of a synthetic'organichomogeneous plastic compound, and provided with longitudinal recessesfor the reception oi' the conductors, as shown in Figs. .4 and 5.

Simultaneously or immediately after the formation of the sleeve byextrusion through a suitable mouthpiece, the corresponding conductorsare positioned in .their respective places and are spiraiiy twistedtogether with the sleeve, whereupon each group oi conductors is providedwith n common external insulation.

The quad-group. thus arranged and twisted, is

passed through another mouthpiece of suitable section, and a commonsheath for the four conductors is extruded, or the group is covered withinsulating material in any other known way.

The drawing shows only three quad-groups, but the cable can or course bemade with any number of conductor or groups.

In Fig. 4, 3 is an insulating sleevearound a quad-group. 4 lrepresentsone or more layers of metal foil, preferably of aluminium. wound aboutone or more layers oi metal tape wrapped around the cable core. 1 is anoutside metal sheath,

, preferably of aluminium, in which latter case it is formed around thecore by a previously annealed tape of aluminium parallel to the core andof such a width that the edges meet and the seam is welded according tothe electrical resistance welding principle, according to which themetal continuously melts or is fused between the electrodes, while thecable is passed through the welding machine. Figs. 6, 7 and 8 show theinsulation around a conductor provided with regular swellings andrecesses, whereby the conductor is kept in the centre of the sleeve.Naturally any other section of sleeve can be embossed on the surfacebetween the conductor and the sleeve, whereby the conductor has aminimum of contact with the insulating material and corresponding lowercapacity.

The insulating foil generally delivered from .the casting machine inbroad continuous tape form. after having passed between special rollsfor embossing, should immediately pass through a cutting machine, whichwill cut the thin foil in the necessary number of foils of desiredwidth.

From the cutting machine the individual foils are passed through aforming machine where each individual foil is formed by means ol amouthpiece into a cylindrical tube around each corresponding electricalconductor, which is passed through the mouthpiece at the same time asthe tube is formed.

When forming the cylindrical insulation tube around the conductor, theedges of the foil overlap and are stuck together by simultaneouslyadding a suitable solvent to one of the edges. whereafter the edges arepressed together and the conductor is now insulated and can, after thesolvent has evaporated, be rolled on a spool.

Should more insulating layers or tubes be needed, the process can berepeated and a conductor already provided with one layer can passthrough another forming machine where more tape-foil is formed and gluedaround the already insulated conductor.

When the capacity of the cable is smaller the tape foil can be placed onspools and be employed in one or more layers in the same way as paperinsulated conductors are now coveredin modern cable works with suicientoverlap with or without application of adhesive to the overlap, or thetubes canbe formed with longitudinal overlapped glued seams parallel tothe conductor, in the same way as in the continuous process abovedescribed. a

Most of the above specified synthetic resins have excellent electricqualities. which specially tit them for insulation purposes.

After the individual conductors have been insulated in any of theabove-mentioned ways', they are twisted in pairs and formed into cablesin known manner, unless special section groups of two or i'ourconductors already twisted are used, in which latter case the respectivegroups are only formed into cables..

If desired. the groups of two. four or more conductors can be providedwith windings oiI metal foil, whereby induction or cross-currentsbetween conductors of different groups is avoided.

The cable once formed is provided with a strip or foil ot thin softaluminium or other suitable metal, wound spirally around the core inorder partly to protect the conductors from outside damage and partly toserve as a shield against induction.

'I'he cable core thus protected may be provided with an outsideinsulation sheath of organic compound, tough and flexible, of suitablecomposition and thickness, which is applied by extrusion or otherwise,such compound being hot and plastic before extrusion and afterwardshardening to a suitable degree of hardness and elasticity. The materialto be employed may be of any of the above specified synthetic resinswhich is sufilciently tough and ilexible to permit of tensioning andbending o! the finished cable.

Should an electrically insulating outside sheath not be necessary, ametal sheath, preferably of aluminium, is applied. A previously annealedtape of aluminium is thus formed around and parallel to the cable core.The longitudinal seam is welded by the electrical resistance weldingprocess, whereby homogeneity and an excellent seam are obtained.

The great advantages possessed by cables made in accordance with thepresent invention are as follows:

'l'he insulating material is a non-hygroscopic one, for instancepolystyrol, ,vinyl-benzene etc.

`In this manner all drying processesare eliminated and there is nodanger of the insulation absorbing moisture from the air.

On account of the good and homogeneous electrical insulation propertiesa better and more constant transmission is obtained than with paperinsulation, and unbalance will be greatly reduced.

It is also possible to increase the distances between repeaters on longdistance communication cables, with resulting reduced costs.

The weight of a ilnished cable is only a small fraction oi' that of acorresponding lead covered cable, which results in low transportationcosts, whilst the whole cable is more easily handled.

Electrolytic corrosion of the sheath is avoided entirely, as a sheath oforganic compound is nonconducting and this circumstance is veryimportant in maintaining a cable plant.

Having now particularly described and ascertained the nature oi vny saidinvention and in what manner the same is to be performed, I 'declarethat what I claim is:-

l. A cable for communication purposes. comprising a flexible insulatingsleeve, a flexible electric conductor enclosed in said sleeve, 'thelatter consisting of a pure polymerization product of a substitutedbenzene, in which each substitute radical comprises a vinyl group, saidpolymerization product being ah unplasticized, synthetic, organicproduct which if, homogeneous, isotropic, and substantiallynon-hygroscopic, and free from hydroxyl groups' 2. The cable claimed inclaim l, in which said substituted benzene is a polymer-izedvinylbenzene.

3. A cable 'for communication purposes, comprising a flexible insulatingsleeve, a flexible electric conductor enclosed in said sleeve, thelatter l consisting oi a pure polymerization product if an aryl olefine,said polymerization product being an unplasticized, synthetic, organicproduct which is homogeneous, isotropic, and' substantiallynon-hygroscopic, and free from hydroxyl ,g1-oups,

4. The cable claimed in claim 3, in which said polymerization productconsists exclusively of polystyrol.

5. An electric quad-cable for communication purposes, comprising anouter insulating sleeve, a plurality of inner sleeves disposed insidethe outer sleeve, a hollow insulating core of substantiallycuadrangular, equilateral cross section disposed inside each one of saidinner sleeves, each insulating core providing recesses between the coreand the surrounding inner sleeve in order to iorm air spaces between thecore and the inner sleeve appert'aining thereto. and a plurality ofelectric conductors disposed in said recesses on each core and at equaldistances from one another to form quad-circuits, whereby a largeportion of each of said conductors is exposed to the surrounding air,the said inner sleeves and cores consisting of a polymerizedvinyl-benzene.

6. A cable for transmission of intelligence and other purposes.comprising an insulating sleeve and an electric conductor disposedinside said sleeve, the latter coml ting of an unplasticized layer ofpolystyrol of suillcient thinness to assure flexibility.

"l, A cable for transmission of intelligence and other purposes,comprising an insulating sleeve and an electric conductor disposedinside said sleeve, the latter consisting of a thin, flexible,unplasticized foil of pure polystyrol.

8. An electric quad-cable for communication purposes, comprising anouter insulating sleeve.

a plurality of inner sleeves disposed inside the outer sleeve,A a hollowinsulating core of substantially quadrangular, equilateral cross sectiondisposed inside each one of said inner sleeves, each insulating coreproviding recesses between the core and the surrounding inner sleeve inorder 4to form air spaces between the core and the inner sleeveappertainlng thereto, and a plurality of electric conductors disposed insaid recesses oneach core and at equal distances from one another toform quad-circuits, whereby a large portion of each of said conductorsis exposed to the surrounding air, the said cores and inner sleevesconsisting of pure, unplasticized polystyrol and the said outer sleeveconsisting oi' metal sur- CERTIFICATE OF CORRECTION Patent No.2,116,615. may 1o, 1958.

HELGE ROST.

It is hereby certified that error appears in the above numhered patentrequiring correctionele follows: In the headingrto the printedspecification, line 5, foreign filing date, for the words "In GermanyFebruary 15, 1952" read In Sweden July 26,1952; and that the saidLetters Patent should be read with this correction therein that the samemay conform to tha recerd of the' ease in the1 Patent Office.

Signed and sealed this 19th day of July, A. D. 1958.

Henry Van rsdale,

(Seal) Acting Commissioner of Patents.

